The present invention relates to a valve for controlling flow of hydraulic fluid, and particularly relates to a power steering control valve for controlling the flow of hydraulic fluid from a pump to a power steering motor.
A known power steering control valve for controlling flow of hydraulic fluid from a pump to a power steering motor includes a valve sleeve having a generally cylindrical bore and a generally cylindrical valve core rotatably mounted in the bore in the valve sleeve. Each of the core and sleeve has a plurality of lands and grooves that cooperate to regulate fluid pressure within the valve and control flow from the pump to the power steering motor.
When the valve core and valve sleeve are in a neutral position, fluid is communicated generally equally to opposite chambers of the power steering motor. When the core and sleeve are relatively rotated from the neutral position, fluid communication with the opposite chambers is variably restricted. Restriction of the fluid communication causes pressurized fluid to be delivered to one of the chambers of the power steering motor to cause motor actuation.
The restriction is provided by the lands on the core and sleeve which define flow orifices of variable size. Relative rotation between the core and the sleeve varies the size of the flow orifices. Upon relative rotation from the neutral position to a displaced position, certain pairs of lands on the core and sleeve radially overlap to restrict the associated flow orifice to the size of a gap between end face surfaces of the respective pairs of lands. Due to a high volume of hydraulic fluid flow from the pump through the flow orifices and pressure changes, noise is generated. The noise includes noise due to cavitation of hydraulic fluid flowing through the flow orifices.